(svn r11399) -Feature(ette): transparency settings can now be saved and thus remembered.

-Codechange: Wrap all transparency settings in accessors, hiding the implementation
-Change: Clicking "transparent building" menu will toggle Houses And Trees only.  The other options can be used in the transparency gui.
Initial patch by Smatz (FS#1349), with some rework by BigBB and your humble servant.

src/openttd.h

@@ -187,17 +187,6 @@ enum {
 	DO_WAYPOINTS          = 6,
 };
 
-enum {
-	TO_SIGNS,
-	TO_TREES,
-	TO_HOUSES,
-	TO_INDUSTRIES,
-	TO_BUILDINGS,
-	TO_BRIDGES,
-	TO_STRUCTURES,
-	TO_LOADING,
-};
-
 /* Landscape types */
 enum {
 	LT_TEMPERATE  = 0,